The goal of this two-year proposal is to test the feasibility of microRNA-based therapeutics as a novel strategy for the treatment of rare cystic kidney diseases. Autosomal recessive cystic kidney diseases include autosomal recessive polycystic kidney disease (ARPKD), renal cysts and diabetes (RCAD), and nephronophthisis (NPHP). These rare genetic disorders are characterized by the formation of cysts in the kidneys and progressive kidney failure. Extrarenal manifestations include congenital hepatic fibrosis (ARPKD), diabetes (RCAD), and blindness (NPHP). Although these disorders are rare with incidences of 1:20,000 or less, they have significant clinical importance. ARPKD and NPHP are the most common monogenic causes of end-stage kidney disease in infants and children. The genes that are mutated in human ARPKD, RCAD, and NPHP have been identified. However, no specific and effective therapies exist for these diseases, and no drugs are currently in clinical trials. Therefore, new therapeutic approaches are needed. For the past 10 years, our laboratory has investigated the molecular pathogenesis of autosomal recessive cystic kidney diseases. We have developed orthologous mouse models carrying mutations in the same genes that are mutated in humans with these disorders. The phenotypes of the mutant mice resemble the phenotypes of affected humans indicating that they represent excellent animal models. Analysis of the mutant mice has helped unravel the pathogenesis of the human diseases and revealed that they are linked in a common pathway. In particular, the transcription factor HNF-1[unreadable], which is mutated in RCAD, regulates the transcription of PKHD1, which is mutated in ARPKD, and GLIS2 and NPHP3, which are mutated in nephronophthisis. Thus, correction of abnormalities in this pathway may be an effective therapeutic approach for cystic kidney diseases. Recent studies have identified microRNAs (miRNAs) as potential molecular targets in human diseases. miRNAs are short, non-coding RNAs that regulate post-transcriptional gene expression by inhibiting translation or promoting cleavage of complementary messenger RNAs. In preliminary studies, we have identified several families of miRNAs that are abnormally overexpressed in HNF-1[unreadable] mutant cells. The sequences of the miRNAs are complementary to mRNAs encoded by known cystic disease genes, such as PKD2 and PKHD1. These studies identify a novel role of miRNAs in the pathogenesis of cystic kidney diseases and suggest that inhibition of miRNAs may be an effective strategy for reducing cyst formation. Recently, effective methods for modulating the activity of miRNAs in vivo have been developed. Antagomirs are chemically modified oligonucleotides that can be administered parenterally and that specifically and durably inactivate target miRNAs. In this proposal, we will use miRNA microarray analysis to comprehensively identify miRNAs that are abnormally expressed in orthologous mouse models of ARPKD, RCAD, and NPHP. Next, we will test whether the administration of antagomirs targeting the overexpressed miRNAs inhibit cyst formation and improve renal function in mutant mice. Such studies would provide important pre-clinical data demonstrating the feasibility of this approach for the treatment of these rare but clinically important genetic disorders and would also have broad implications for the treatment of other rare disorders affecting the kidney. PUBLIC HEALTH RELEVANCE: Autosomal recessive cystic kidney diseases are rare genetic disorders that produce kidney failure in children. No specific treatment currently exists. This proposal will test the feasibility of treating these disorders using a new technology, microRNA-based therapeutics.